Background: Delineating mechanisms of alloantibody formation and maintenance could guide development of novel therapies aimed at treating antibody mediated transplant rejection. Published work from 2011 suggested that eosinophil-produced cytokines are essential for survival of nominal antigen-specific plasma cells (PC) in the bone marrow (BM) raising the hypothesis that eliminating eosinophils could be effective in preventing or treating alloantibody mediated graft injury.

Methods: We sensitized eosinophil-deficient B6 and Balb/c mice (GATAmut, with an induced mutation in GATA3 promoter) with ip injections of allogeneic splenocytes (SCs, 10×106/week for 3 wks) or with allogeneic heart grafts. Kinetics and titers of serum donor-specific antibodies (DSA) were assessed. Quantification of CD130+B220low PC populations in the BM and spleen were assessed by flow cytometry.

Results: NaÏve GAT3mut Balb/c mice contained no detectable eosinophils in BM or spleen, had similar percentages of BM PC, but more spleen PC than WT controls (0.39±0.08 vs. 0.43±0.05%, n.s. and 0.68±0.08 vs. 0.42±0.07%; p<0.05, respectively). After sensitization with B6 SCs, we observed fewer BM PC but more spleen PC in the Balb/c GATA3mut mice vs. controls (0.370.12% vs. 0.54±0.12%, p<0.05 and 0.28±0.14% vs. 0.57±0.21%; p<0.05, respectively). The frequencies and activation statuses of peripheral CD4 and CD8 cells as well as B cells were not different between groups. 12 weeks after sensitization with B6 SCs, we observed modestly reduced serum DSA in Balb/c GATA3mut mice vs. WT (% binding at 1:500 dilution: 6.0±4.9 vs. 11.1±5.1%; p<0.05, n=14/grp). We did not observe differences in DSA between groups after heart allograft rejection (30.5±1.7 vs. 27.4±7.3%; n.s. at 12 weeks, n=7/group, rejection occurred by d8 in both groups). To test whether absence of eosinophils impacts DSA induction following a secondary challenge, 3 mo after heart graft rejection and documentation of equivalent posttransplant DSA, we immunized groups of WT and GATA3mut with donor SC ip. Kinetic analyses revealed DSA increased significantly in both groups but without differences between groups. Repeat experiments in B6 WT and GATA3mut mice yielded similar results.

Conclusions: In contrast to the reported requirement for eosinophils in the maintenance of plasma cell reactive to nominal antigens, our data indicate that eosinophils regulate the distribution of plasma cells between BM and periphery, but are not required for induction or maintenance of alloantibodies.

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